1、 Rec. ITU-R F.1612 1 RECOMMENDATION ITU-R F.1612 Interference evaluation of the fixed service using high altitude platform stations to protect the radio astronomy service from uplink transmission in high altitude platform station systems in the 31.3-31.8 GHz band (Question ITU-R 230/9) (2003) The IT
2、U Radiocommunication Assembly, considering a) that new technology utilizing high altitude platform stations (HAPS) in the stratosphere is being developed; b) that WRC-97 made provisions for operation of HAPS within the fixed service in the bands 47.2-47.5 GHz and 47.9-48.2 GHz; c) that since the 47
3、GHz bands are more susceptible to rain attenuation in those countries listed in Nos. 5.537A and 5.543A of the Radio Regulations (RR), the frequency range 18-32 GHz has been studied for possible identification of additional spectrum in ITU-R; d) that WRC-2000 made a provision for the use of HAPS in t
4、he fixed service in the bands 27.5-28.35 GHz and 31.0-31.3 GHz in certain countries on a non-harmful, non-protection basis in order to address issues of rain attenuation associated with the 47 GHz bands (RR Nos. 5.537A and 5.543A). Until WRC-03, since the 31.3-31.8 GHz band is allocated to the radio
5、 astronomy service (RAS), Earth exploration-satellite service (EESS) (passive) and space research service (passive), use of the band 31.0-31.3 GHz is limited to the lower half of the band (31.0-31.15 GHz); e) that Resolution 122 (Rev.WRC-2000) requests urgent studies on technical, sharing and regula
6、tory issues in order to determine criteria for the operation of HAPS in the bands referred to in considering d) above; f) that it is necessary to protect appropriately the RAS, EESS (passive) and space research service (passive), taking into account RR No. 5.340 and the interference criteria given i
7、n Recommendations ITU-R SA.1029 and ITU-R RA.769, recommends 1 that the methodology in Annexes 1, 2 and 3 should be used for the evaluation of interference by HAPS uplinks to the RAS in the frequency band 31.3-31.8 GHz; 2 that the location of HAPS airships and HAPS ground stations relative to the RA
8、S station should be chosen to protect the RAS from unwanted emissions in the HAPS uplink in the 31.3-31.8 GHz band; 2 Rec. ITU-R F.1612 3 that in order to protect the RAS station from unwanted emissions via the HAPS uplink in the 31.3-31.8 GHz band, one or more spot beam cells around an RAS station
9、should be excluded from the service area of the fixed service using HAPS. NOTE 1 Recommendation ITU-R F.1569 contains typical parameters describing the HAPS system for the evaluation of the impact of unwanted emissions on the RAS in the 31 GHz band. NOTE 2 The aggregate interference from fixed servi
10、ce, including HAPS, needs to be considered. Annex 1 Typical parameters of the RAS and a model to be used for impact evaluation from HAPS ground station on the RAS station 1 Parameters of uplink transmission in HAPS system The parameters regarding HAPS systems are based on Recommendation ITU-R F.1569
11、 (altitude: 20-25 km, minimum operational elevation angle: 20, and in rainy conditions). The footprint formed by a spot beam is referred to as a cell. A frequency reuse factor of four is adopted in this study, that is, the available frequency band of 300 MHz (31.0-31.3 GHz) is equally divided into f
12、our sub-bands of 75 MHz which are used simultaneously for uplink transmissions in multiple cells. An automatic power control scheme is adopted in the uplink, in which the power is increased or decreased by 6 dB, depending on weather conditions. The level of out-of-band emissions in a HAPS uplink use
13、d in this study is 100 dB(W/MHz) under rainy conditions, assuming that automatic transmitting power control is being used in the uplink. The derivation of the out-of-band emission level is described in 11 of Recommendation ITU-R F.1569. 2 Parameters of RAS The parameters of RAS antennas used in this
14、 study are shown in Table 1. It is assumed that the RAS antenna is pointing at the azimuth of the HAPS ground station, at the minimum operational elevation for that particular radio telescope. The gain of the receiving antenna for the interference is calculated using Recommendation ITU-R SA.509 for
15、the separation angle of more than 1 between the boresight direction of RAS antenna and the direction of arrival of the interference. Rec. ITU-R F.1612 3 TABLE 1 Parameters of RAS antennas used in this study 3 Interference evaluation model 3.1 Single entry Figure 1 shows the interference evaluation m
16、odel for one HAPS ground station and one RAS station. It is assumed that HAPS ground station is located in the same plane as the RAS station. Two situations are considered regarding the antenna boresight direction of HAPS ground station. One is that the antenna of HAPS ground station faces to the RA
17、S station in azimuth (worst case in the single entry scenario) and the other is that the antenna of HAPS ground station is directed at an azimuth 180 away from the direction of the RAS station. It is assumed that the RAS antenna is being operated with the minimum operational elevation angle in both
18、cases. 1612-012020dHAPSRAS station Two models of HAPS ground stationsat the same altitude of RAS stationFIGURE 1Interference from a HAPS ground station to a RAS station (single entry case)Minimum operationalelevation angleInterferenceFaces to RAS station Faces against RAS stationGmax(dBi) Diameter (
19、m) Altitude (km) Minimum operational elevation angle (degrees) Nobeyama (Japan) 81.2 45 1.35 15 Taeduk (Korea) 70.9 13.7 0.12 15 Delingha (China) 70.9 13.7 3.2 5 4 Rec. ITU-R F.1612 3.2 Aggregate interference from multiple HAPS stations As shown in Fig. 2, the following models and assumptions are us
20、ed for the evaluation of aggregate interference: four HAPS ground stations are located in the centre of each service cell and all the antennas point to the corresponding HAPS airship (total bandwidth of 300 MHz (31.0-31.3 GHz), frequency reuse of four times and signal bandwidth of 20 MHz are assumed
21、); the aggregate interference is obtained by summing a parameter defined as the “received interference pfd at RAS station” plus “receiving RAS station gain for the interference” for all HAPS ground stations (= 367 cell 4 stations 3 HAPS service area); the out-of-band emission power of 100 dB(W/MHz)
22、is assumed from each HAPS ground station; the RAS antenna is located at between the boundary, A, of the three HAPS service areas and the nadir point O; RAS antenna located at point B directs A or O in azimuth. It is assumed that the RAS antenna is at the lowest elevation angle at which observations
23、are made using that instrument (5 or 15). 1612-02S2S1OBAXYS3RAS antenna5 or 155 or 15FIGURE 2Model example for aggregate interference evaluationA: boundary of three HAPS service areasB: location of RAS antenna on segment AOO: nadir point of HAPSS1: main areaS2S3: sub areaRAS antenna located at point
24、 B directs A or O in azimuth.Rec. ITU-R F.1612 5 Annex 2 Propagation model and protection criteria of RAS 1 Propagation model According to Recommendation ITU-R P.452, 4.2, the propagation loss between stations on the surface of the Earth not exceeded for time percentage, p% is given by: gsbApEdfpL +
25、= )(log20log205.92)(0dB (1) where: f : frequency (GHz) (31.3 is used in this study) d: path length (km) Es(p) : correction for multipath and focusing effects )50/log()e1(6.2)(10/ppEds= dB (2) Ag: total gaseous absorption (dB) dAwg)(0+=dB (3) where: 0, w() : specific attenuation due to dry air and wa
26、ter vapour, respectively, and are found from the equations in Recommendation ITU-R P.676 : water vapour density += 5.25.73g/m(4) : fraction of the total path over water. In this study, the factor of gaseous absorption Agis assumed to be 0 in order to consider the worst case of interference. 2 Protec
27、tion criteria of RAS Recommendation ITU-R RA.769 provides the threshold spectral pfd to protect the RAS (calculated for an antenna gain of 0 dBi). This methodology gives pfd levels of 168 dB(W/(m2 MHz) in the band 31.3-31.8 GHz. In order to take the effect of the receiving antenna gain into account,
28、 the value of “interference pfd received at RAS antenna” plus “receiving RAS antenna gain for the interference” is adopted as the protection criteria of RAS and the required separation distance is obtained by the need to meet the Recommendation ITU-R RA.769 criterion 168 dB(W/(m2 MHz). 6 Rec. ITU-R
29、F.1612 Annex 3 Impact of HAPS ground station on RAS station 1 Interference evaluation 1.1 Single entry Under the conditions described in Annexes 1 and 2, the impact (received pfd + RAS antenna gain) of one HAPS ground station is calculated as function of the distance between the RAS station and HAPS
30、 ground station. Recommendation ITU-R F.1245 is used for the antenna radiation pattern of HAPS ground station. The results for Nobeyama (Japan), Taeduk (Korea) and Delingha (China) are shown in Figs. 3 and 4 for time percentage of 0.001%, 1% and 10%. The results obtained by using free space propagat
31、ion model are also shown for the reference. Required separation distance is obtained by the intersecting point of the obtained curve and the protection criterion of RAS: 168 dB(W/(m2 MHz). Table 2 summarizes the required separation distances for several values of time percentage. The required separa
32、tion distances, when the RAS antenna and HAPS ground station direct face-to-face in azimuth (denoted by forward), are 0.9 km for Nobeyama and Taeduk and 3.94 km for Delingha even when the free space propagation model and the time percentage of 1% are assumed. Separation distances when the antenna of
33、 HAPS ground station is directed 180 away from the direction to RAS station are also shown as references (denoted by backward). The required guardband is calculated by using the example IF filter and equation (3) described in 11 in Annex 1 of Recommendation ITU-R F.1569. The thermal noise level at t
34、he input of RF module is used as the minimum level to determine fpmt. The width of the required guardband is 10 MHz for 20.2 MHz IF filter bandwidth (3 dB). This guardband depends on the signal bandwidth and the attenuation characteristics of the IF band-pass filter. 1.2 Aggregate interference In th
35、e case of the aggregate interference under the condition described in 3.2 in Annex 1, it is assumed that there are no HAPS transmissions in the cell including the RAS station. Figures 4a) to 4d) show the total weighted value of “received pfd” plus “RAS antenna gain”, where the RAS antenna is pointed
36、 at the point A or O. Furthermore, the minimum operational elevation is 15 or 5 and “Y coordinate of RAS” shows the distance of RAS antenna from the nadir point O. The terms “main area” and “sub area” are defined in Fig. 2. As shown in these Figures, the aggregate value of “received pfd” plus “RAS a
37、ntenna gain” does not exceed the permissible interference criterion of RAS of 168 dB(W/(m2 MHz) except for the case of Fig. 4d). Figure 4d) which is a certain special case for an antenna elevation 5, shows that the total “received pfd” plus “RAS antenna gain” exceeds the protection criterion. Such a
38、 result occurs since both RAS antenna and HAPS ground station antenna direct face-to-face with short separation distance. Rec. ITU-R F.1612 7 TABLE 2 Required separation distances between HAPS ground station and RAS station for the case of single entry 1612-031901801701601501401301201234567200190180
39、170160150140130120012345672000pfd +RAS antennagain(dB(W/(m2 MHz)Distance from HAPS ground station to RAS antenna (km)pfd +RAS antennagain(dB(W/(m2 MHz)Distance from HAPS ground station to RAS antenna (km)Rec. ITU-R P.452, 4.2 (p = 10%)Rec. ITU-R P.452, 4.2 (p = 1%)Rec. ITU-R P.452, 4.2 (p = 0.001%)F
40、ree space lossProtection criteria of RASProtection criteria of RASa) Nobeyama (Japan) and Taeduk (Korea)minimum elevation = 15b) Delingha (China) minimum elevation = 5FIGURE 3Received pfd plus RAS antenna gain at RAS station over line-of-sight whereRAS station and HAPS ground station direct face-to-
41、faceRequired separation from a HAPS ground station (km) Direction(1)Time percentage p (%) 0.001 1 10 Forward Line-of-sight (including aggregate) 0.99 0.90 0.88 Nobeyama, Taeduk Backward Line-of-sight (including aggregate) 0.31 0.30 0.30 Forward Line-of-sight (including aggregate) 6.38 3.94 3.56 Deli
42、ngha Backward Line-of-sight (including aggregate) 1.36 1.21 1.17 (1)Forward: the antenna of HAPS ground station is faced to the RAS station. Backward: the antenna of HAPS ground station is against the RAS station. 8 Rec. ITU-R F.1612 1612-0419519018518017517016516050 40 30 20 10 0 102001951901851801
43、7517016516060 50 40 30 20 10 0 102006019519018518017517016516050 40 30 20 10 0 1019018518017517016516060 50 40 30 20 10 0 1020060pfd +RAS antennagain(dB(W/(m2 MHz)Y coordinate of RAS (km)pfd +RAS antennagain(dB(W/(m2 MHz)Y coordinate of RAS (km)Main areaSub areaAggregatea) RAS antenna directs point
44、Oelevation angle of RAS antenna = 15b) RAS antenna directs point Aelevation angle of RAS antenna = 15FIGURE 4pfd plus RAS antenna gain in the case of aggregate interferencepfd +RAS antennagain(dB(W/(m2 MHz)Y coordinate of RAS (km)pfd +RAS antennagain(dB(W/(m2 MHz)Y coordinate of RAS (km)c) RAS anten
45、na directs point Oelevation angle of RAS antenna = 5d) RAS antenna directs point Aelevation angle of RAS antenna = 5Rec. ITU-R F.1612 9 Figure 5 shows plots of interference level of “received pfd” plus “RAS antenna gain” from the HAPS ground station in each spot. The interference of the HAPS ground
46、stations in the neighbouring cell at the boresight direction of RAS antenna is the largest one, which is 166.1 dB(W/(m2 MHz). If such HAPS ground stations (or cells) causing such high levels of unwanted emissions are prohibited from operating, the aggregate interference will not then exceed the prot
47、ection criterion. It must be pointed out however that in aggregate interference cases, the total unwanted emission power received at the radio telescope depends on the mode of operation of the RAS station and the design of HAPS network and that general conclusions cannot be obtained. 1612-0524021020
48、019018016060 40 20 0 20 40 60170220230pfd +RAS antennagain(dB(W/(m2 MHz)X axis (km)FIGURE 5Plots of received pfd plus RAS antenna gain for each HAPSground station in the case of Fig. 3d) wherethe value of Y coordinate distance is 49.1 km(all interference values are projectedto X axis, where X axis i
49、s defined in Fig. 2)2 Summary Study results indicate that HAPS systems should be deployed under the following conditions to protect a radio astronomy station: HAPS airships should not be located in the vicinity of a RAS station in order to avoid the situation where many HAPS ground stations are pointing in azimuth towards the RAS station; the fixed service using HAPS should not o
